My thoughts and perspectives on health, science, and logic… Keep an open mind!

Posts tagged ‘torque’

Few exercises in the gym are as loved and as hated as the ever-present squat. If you’ve spent any length of time in the exercise world, you’ve undoubtedly encountered countless individuals who swear by the practice of grabbing a bunch of weight and dropping their butts to the ground. Many more engage in the practice sans weight (just think about how many 30-day fitness challenges involve bodyweight squats). Whatever the flavor, it’s pretty widely accepted that squats are the “go-to” exercise for building the derriere of your dreams. While I COULD spend this entire post picking apart some of those misconceptions, I’ll save that for another day. Instead, I’ll assume that you’ve determined that this movement is appropriate for your body and goals and get right to the meat of this write-up. That is, a comparison between TWO TYPES of squats.

— Allow me to interject before we go any further that I am not a big fan of sticking labels on exercises and saying, “THIS is the way it must be done!” At the end of the day, such an approach is inappropriate if you’re trying to tailor an exercise to a particular body for a specific goal. BUT, in the spirit of simplicity, I’ll make some generalizations so I can get some basic points across. —

Now that that’s cleared up, let’s continue. The main focus of this post is to look at the difference between the back squat and the front squat in terms of how they might load the different joints and musculature of the body. While both movements certainly challenge the legs, hips, lower back, etc. to some degree; the exact amount of effort required at each region of the body will change depending on exactly where you put the weight and how your joints move. To give some understanding of this, we need to understand what joints are going to be moving during a squat-like exercise in the first place. The list of main players, in no particular order, will be as follows as we descend during a squat:

1.) Ankles — Increasing dorsiflexion (shin moves toward the top of the foot)

2.) Knees— Increasing flexion (knees bending, smaller angle between the calf and back of the thigh)

3.) Hips— Increasing flexion (torso and fronts of the thighs get closer together)

*.) On the way up (coming out of the squat), these movements will necessarily be reversed!

** NOTE ** I’m assuming a bunch of other joints are able to stay still during the motion. If you can’t keep the rest of the body relatively stable during this exercise, then you shouldn’t be doing it! I’m also not mentioning motion of the intrinsic joints in the foot, as such a discussion is beyond the scope of this post. We could spend all day talking about how the foot does or doesn’t move during different activities.

Anyway, all exercises that are traditionally known as a squat will include movement at the 3 joints listed above. The question is how MUCH movement will occur! That will depend on a bunch of different factors that I’ll try to hint at here. Let’s start by looking at a diagram of three different squat scenarios. On the left is a low-bar back squat (where the bar is kept relatively low on the back, as the name implies). In the middle is a high-bar back squat (I’ll let you figure out why it’s called that). And on the right is a front squat:

Much thanks to Lon Kilgore for the illustration. Note the different body angles between the different squat configurations (Low bar, high bar, and front).

WARNING — SCIENCE AHEAD!!!

So — What do you notice? In each scenario, the hip, knee, and ankle are obviously bending. But do you notice how the angles are all markedly different? That’s worth taking a moment to appreciate. This is due to a little thing called PHYSICS! Specifically, the center of mass of your body (including the weight you’re lifting) has to stay over your base of support in order for you not to fall over. Let me say that again:

Your CENTER-OF-MASS must stay over your BASE OF SUPPORT to stay upright!!!

Your center of mass refers to the point about which all of your body mass is distributed. If you averaged the positions of ALL of the mass you have, that hypothetical average “spot” is where the center of mass would be. It’s also called the center of gravity. If this falls outside of your base of support, you can’t stay upright. In the case of a standing exercise, that base of support is your feet! So the bar plus your body weight will need to be balanced over your feet for you to remain standing (or “squatting”). In the pictures above, you can think of that vertical dashed line as passing through the center of mass. Notice that it’s over the feet in all three cases. So when you move the bar farther forward or backward, you also have to adjust your body position to compensate and KEEP that line from falling in front of or behind your feet.

If you have to hold your body in a certain position for the lift when the bar is on your back (picture on the left), it should make sense that you’ll have to lean backward more if you decide to put the bar IN FRONT of your body instead (picture on the right). Think about it — you’ve just put more weight in front, so you have to bring some of the weight back somehow to keep yourself balanced over your feet. A great way to do that is to sit more upright. And that’s exactly what we see in the front squat picture. Notice also that sitting upright means that we have to bend differently at the knees, hips, and ankles if we want to get down into the bottom position. Look at the angles in the picture closely! If we have LESS hip flexion, we have to make up for it by having MORE knee flexion and ankle dorsiflexion. This coordinated movement has to occur for us to get into the bottom position effectively. Keep that in mind 🙂

So you can see that you’ll have to adjust your body position to accommodate the way you’re holding the weight. If the weight moves, the body has to move as well. You do this all the time when you carry things and move around in a typical day. Most of the time, you probably don’t even notice!

Alright, that’s all well and good. We’ve established a basic understanding of how the body can move to adjust to different bar positions. But what does that really mean in terms of what muscles get used? To explain this, I need to throw another picture at you. This picture will be similar to the previous one, but it points out another aspect that I haven’t yet talked about:

Edited image gratefully borrowed from barbellacademy.com — Note the distances between the hip and knee joints and the dashed vertical line of force.

So here you see three pictures that are similar to the ones in the previous image. But instead of joint angles, we’re pointing out something different. See the horizontal lines coming from the knee and hip joints at each squat position? They help us to visualize how far those joints are from the line of force (that dashed line representing body weight and the bar in this case). That distance — the blue line for the hip, and the green line for the knee — is known as the moment arm for the joint. It’s the perpendicular distance between the axis of rotation (the pivot point or joint in this image) and the line of force being applied to it. If that all sounds kind of wordy, think of it this way:

How does a wrench work? It is a tool that lets you grab onto a nut or a bolt and turn it. And we all know that a longer wrench makes it easier than a shorter one. But why? The answer is simple — the longer wrench has a longer moment arm. That’s important, because the amount of torque (rotational or turning force) that you generate at a joint or axis (the bolt you’re trying to turn, in the wrench example) is directly related to how far away the force you’re applying is. A long wrench gives you a longer lever, which means you can apply force to turn the bolt from farther away. That imparts a greater torque to the bolt, making it easier for you to turn it!

So taking that logic back to the squat example, what do we see? When the joints are farther away from the weight, we can see that the weight will generate more torque at those joints. That means the weight has a greater mechanical advantage to cause those joints to move (hip and knee flexion, in this case). So if we’re trying to lift the weight, that means that OUR MUSCLES have to generate more force to oppose that weight. So if the weight on the bar stays the same, then moving a joint farther away from that imaginary dashed line in the picture will make our muscles work harder at those joints! We can see that the front squat creates the greatest moment arm at the knees in this picture, while the low bar back squat creates the greatest moment arm at the hips.

With that understanding, we can then say the following (assuming we haven’t altered anything else about the lifts):

1) A front squat will tend to require more work at the knees, AND

2) a back squat (particularly with a lower bar) will tend to require more work at the low back/hips

END OF SCIENCE-Y STUFF!

So there you have it — a somewhat wordy explanation for WHY a back squat is different from a front squat. Note that this is still EXTREMELY simplified, and there are many other factors that can further affect how these movements challenge your body. People with different body segment lengths will “fold up” differently, and some people have much more joint range at the hips, knees, and ankles than others. As such, not everyone will be able to achieve the same depths or positions. That’s okay! But if you understand some of the basics behind body mechanics, you’ll be better equipped to understand why that is and what might be the best approach for your workouts. There are also different artificial tools that can affect a squat — such as lifting shoes, Smith machines, hack squat machines, etc. So this is just scratching the surface!

Finally, this was just looking at some basic joint mechanics and trying to appreciate how the major body segments are moving in relation to one another. Want to know how that affects specific muscles in the hips and legs? Stay tuned for a future entry that will examine some of the muscular anatomy of the area and give a little insight into what’s actually responsible for lifting you (and that bar!) up off of the floor!